1. Field of the Invention
The invention relates to a device comprising a multiphase load and a static converter with a multiphase output for supplying the load, as well as inductance coils which are each allocated to a phase and wound in the same direction and with the same number of windings on a common magnetic core to form a closed magnetic circuit.
Such a device may, for example, be used for operating a multiphase asynchronous motor as load, i.e. as a driving means. Basically, such a device may also be used with loads comprising inductive energy storage means, such as longer connective leads, with magnetic vibrators, piezoelectric resonators and the like.
2. Discussion of the Prior Art
In a driving means with a multiphase asynchronous motor as load, the burden on the driving means' components during operation at particularly high revolutions is basically impaired by the deficiencies in the electromagnetic symmetry of the asynchronous motor and/or the converter's connected semiconductor output stages. This was not of importance as long as the above mentioned high revolutions and the respective dynamic ratio were not required and, in addition to this, there was no necessity for creating the prerequisites for high-performance bearing of the motor's shaft, in particular by magnetic bearing. Present high-speed drive technology makes increased demands on the dynamics of the driving means, which no longer allows magnetic forces to act vertically on the shaft. Therefrom a completely different and new behaviour on the part of the asynchronous motor's rotor arises, in particular concerning its dynamics, critical speed and bearing stresses. Such a driving means is, for example, known for the patent application PCT/CH89/00188.
The same applies to the other loads mentioned above, i.e. loads with inductive energy storage means, such as longer connective leads, with magnetic vibrators, piezoelectric resonators and the like.
The converter output of such a device, in particular of such a driving means, is sensitive to high electrical spikes of a high frequency. Consequently the converter's reliability has to be maintained, in particular in highly dynamical operating modes with highly saturated loads, i.e. when the energy requirements and the direction of the energy flow (acceleration and breaking) change rapidly with the respective burden on the converter's recovery diode caused by switching processes. The respective presently known safety measures are not adequate for protecting the converter's semiconductor output stages. Furthermore, they generate electrical losses and thus reduce the efficiency of the device, or the driving means respectively.
Additionally, deficiencies in the load's and the converter's electromagnetic symmetry cause a burden on the load's support. The device must be able to cope with and overcome the forces and irregularities caused by this burden, whereby critical frequencies are not dampened and filtered out. In a driving means with a multiphase asynchronous motor as load, the deficiencies in the electromagnetic symmetry of the asynchronous motor and the converter constitute a burden for the asynchronous motor's bearing. The forces and irregularities caused by this burden must be borne by the bearing and must be overcome by the driving means' components, whereby critical speeds are not dampened or filtered out. From filtering technology and, for example, from EP-0300872 it is known to suppress interference arising in the phase leads, which occurs in a three-phase power supply in form of spikes, by means of coils which are wound in one direction around a single-aperture core. In this context the use of a single-aperture core for high frequencies or a U-I-lamella core is known, for example, from JP-54-144851.